The present invention relates to a wrap-around braking device for a planetary gear train, especially for a 2-gear planetary gear train, as well as a planetary gear train, especially a 2-gear planetary gear train, having a wrap-around braking device.
From WO 02/093034 A2, a wrap-around braking device or a band brake for braking a brake drum is known. The band brake has a threaded spindle mounted in a floating manner with a right-hand thread and a left-hand thread. A brake band that wraps around the brake drum is attached by two nuts both on the right-hand thread and also on the left-hand thread. The rotation of the threaded spindle by an electric motor moves the two nuts toward each other, wherein the brake band contacts the brake drum and brakes this drum, or away from each other, wherein the brake band is opened and the brake drum is released.
Between the threaded spindle and the brake drum there are housing-side stops that are arranged opposite each other in the axial direction of the threaded spindle, so that brake band-side ends of the nuts or threaded spindle-side ends of the brake band contact these stops. In this way, the actuation force or the actuation moment that is exerted on the threaded spindle by the electric motor can be reduced, because the rotation of the brake drum by means of the brake band and the housing-side support by the corresponding stop generate a self-reinforcing effect, wherein the effective braking force is increased.
In WO 02/093034 A2, however, it is a disadvantage that the threaded spindle must have both a right-hand thread and also a left-hand thread, and thus must have a very complicated production. The floating mounting of the threaded spindle further requires serration on at least one of its axial ends, in order to be able to transmit the torque of the electric motor to the threaded spindle.